Soybean rich diets have long been touted to have various health benefits, including boosting heart health, serum cholesterol reduction, lowering the risk of cancer, cancerous or tumor cell inhibition, improving woman's bones and health, and stimulation of the immune system. In addition, the soybean amino acid profile is one of the most complete among vegetable protein sources, and resembles (with the exception of sulfur-containing amino acids) the general patterns derived from high-quality animal protein sources. However, soy has not been widely used in various food products because the indigenous problems of soy off flavor, poor solubility and texture.
On Oct. 26, 1999, the FDA accepted scientific evidence that suggests a reduction in the risk of coronary heart disease from soy protein enriched low-fat, low-cholesterol diets, and approved health claims for labeled food products that link intake of at least 6.25 grams of dietary soy protein per reference customarily consumed amount of the food product to a possible reduction in the risk of heart disease. This has intensified efforts to incorporate soy into a wide variety of foods. The benefit of soy protein may be related to its antioxidant activity (see, e.g., Chen et al., J. Agric. Food Chem., 46:49-53 (1998); Chen et al., J. Agric. Food Chem., 43:574-578 (1995); Chen et al., J. Agric. Food Chem., 43:574-578 (1996); Suetsuna, Jpn. Soc. Nutr. Food Sci., 52:225-228 (1999); and Zhang et al., Ann. NY Acad. Sci., 864:640-645 (1998)). By scavenging free radicals and oxidative species generated during the course of in vivo reactions, the peptides may help protect against pathogenic processes involving enzyme inactivation, DNA mutation, and/or protein denaturation (see, e.g., Szweda et al., J. Biol. Chem., 268:3342 (1993); and Reiss et al., Biochem. Biophys. Res. Commun., 48:921 (1972).
While soy is useful in food products, it is well known that soy products have undesirable odors and flavors that must be removed in order to make the soy materials useful. It is believed that lipoxygenases catalyze the oxidation of certain polyunsaturated fatty acids, producing hydroperoxides which are degraded into volatile carbonyl compounds, associated with objectionable odors and flavors in soy-derived materials.
Additionally, while the protein content of soy-derived materials is considered valuable, the soluble carbohydrates are considered undesirable. Their removal from soy protein fractions is an objective in many processes in which the proteins are recovered. Another undesirable compound in soy proteins are phytates, which are calcium-magnesium-potassium salts of inositol hexaphosphoric acid. Such compounds are believed to chelate metal ions and are not readily absorbed by the human body. They are considered to bind to soy proteins and interfere with digestion, thus removal of phytates in soy-derived materials is advantageous.
Generally, untreated forms of soy protein are not readily soluble in aqueous liquids, and are difficult to incorporate into various food products, particularly beverages. Soy proteins often have low solubility at pH values of about 6.5 to about 8.5 and often precipitate out at pH values of about 3.5 to about 6.5, thereby imparting a cloudy appearance and/or a gritty or sandy texture to the target food product. Another major problem associated with soy protein is soy off flavor. Further, untreated soy protein does not generally have significant antioxidant activity although it does contain antioxidant components (e.g., isoflavones) which are associated with or bonded with the soy protein.
Attempts to improve the solubility and other functional properties of soy protein primarily involve hydrolysis. However, soy protein is known to have an undesirable flavor profile, and attempts to hydrolyze soy protein often produce a bitter hydrolysate. While not bound by any particular theory, it is believed that the bitter taste stems from excess low-molecular fractions and accumulated hydrophobic peptides from the hydrolysis. In previous endeavors, undesirable hydrolytic fractions were avoided at the price of substantial processing inefficiencies which reduced the degree of hydrolysis. In other words, the foregoing soy protein hydrolyzing methods avoided low-molecular fractions by early termination of the process, thereby suffering low yields of usable product.
Therefore it would be advantageous to develop a process that hydrolyzes a soy protein to deliver a high yield of soluble protein. Further the soluble protein should contain a high amount of protein (for example, 6.25 g soy protein/serving or higher) that can be introduced into a neutral or low pH product. It would also be advantageous to utilize crude soy material (e.g., defatted soy flour, soy meal after oil extraction, or other soy materials containing significant levels of fiber) in an effective manner to obtain highly functional soy protein which can be used in a variety of food products.